Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a first image of a display screen or portion thereof with transitional graphical user interface; and,

FIG. 2 is a front view of a second image of the display screen or portion thereof with transitional graphical user interface.

The outermost broken-line perimeter illustrates a display screen portion and forms no part of the claimed design. The remaining broken lines illustrate portions of a graphical user interface and form no part of the claimed design. The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-2. The process or period in which one image transitions to another image forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 